Refrigerant system with pulse width modulation control in combination with expansion device control

ABSTRACT

A refrigerant system is provided with pulse width modulation control to adjust the amount of refrigerant compressed by a compressor. In one embodiment, a pulse width modulation control controls a suction modulation valve cycled between open and closed positions. In a second embodiment, the compressor itself is cycled between a position at which it compresses refrigerant and a position at which the compression elements are disengaged. In either embodiment, the control also cycles the expansion device in concert with cycling the pulse width modulation valve or the compressor. In this manner, pressure fluctuations in the refrigerant system do not exceed desirable levels. Typical cycle time for pulse width modulation control is between 5 and 30 seconds, and typical offset (delay) time for an expansion device may be between 0 and 3 seconds.

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system, wherein the capacityof the refrigerant system is adjusted by a pulse width modulationcontrol, and a main expansion device of the refrigerant system is usedto limit or eliminate refrigerant flow communication between anevaporator and a condenser when a pulse width modulation control ispreventing compression of a refrigerant or blocking, at least partially,refrigerant flow from entering into a compressor.

One method that is known in the prior art to assist in the adjustment ofcapacity provided by a refrigerant system is the use of a pulse widthmodulation control. It is known in the prior art to apply a pulse widthmodulation control to rapidly cycle a valve between open and closedpositions for controlling the flow of refrigerant through therefrigerant system to adjust capacity. Therefore, by limiting the amountof refrigerant flow passing through the system, the capacity can bereduced below a full-load capacity of the refrigerant system. There aremany ways of applying pulse width modulation technique to variouscomponents to reduce refrigerant system capacity. For instance, a valvelocated at the compressor suction can be cycled in a pulse widthmodulation manner or compression elements themselves can be engaged anddisengaged at a certain rate.

One challenge raised by the prior art use of pulse width modulationcontrols is that while this technique does provide control overrefrigerant system capacity, the suction and discharge system pressurescan experience undesirably large fluctuations, for instance, between the“on” and “off” positions of the pulse width modulation valve. Suchpressure fluctuations are undesirable and may make it difficult tocontrol the operation of various system components. Also, it may becomeharder to maintain constant parameters, such as temperature andhumidity, within the environment to be conditioned. Furthermore, theoverall system operation may become less efficient due to irreversiblelosses associated with these pressure fluctuations.

On the other hand, if the pulse width modulation valve is cycled toofrequently to minimize the pressure fluctuations, there are additionalcycling losses associated with a transition of certain system componentsfrom the state at which the valve is open to the state at which thevalve is in a closed position. Further, the chances of valve failureincrease due to the extensive cycling.

As was mentioned above, there is another known way of using pulse widthmodulation approach to engage and disengage the scroll compressorcompression elements. This is done by rapidly changing refrigerantpressure in a scroll compressor back pressure chamber. When pressure islow in the back pressure chamber, then the scroll compressor members areallowed move out of contact with each other and there will beeffectively no refrigerant compressed. On the other hand, when pressureis high in the back pressure chamber, the scroll elements are engagedwith each other and provide full compression of the refrigerant flowingthrough the compressor. The abovementioned problem of the suction and/ordischarge pressure fluctuations associated with this control may beundesirable and create problems with proper system operation.

In another control for an HVAC&R system, the pulse width modulationcontrol can be provided for the pulse width modulation of scrollelements by separating the elements and bringing them back into contactwith each other in a pulse width modulated manner where the control willmonitor pressures or temperatures on the suction (low pressure) side,and adjust the pulse width modulation duty cycle accordingly. However,this disclosed control does not specifically seek to minimizefluctuations, associated conditioned space discomfort and efficiencylosses, as well as it does not control a suction pulse width modulationvalve, and also does not monitor conditions on the discharge (highpressure) side of the system.

It is known in the prior art to include an isolation valve between theevaporator and the condenser to block flow between the two componentswhen it is used in conjunction with pulse width modulation of the scrollelements. In this case, the isolation valve is normally closed when thecompressor is not compressing a refrigerant. This solution requires theinclusion of a separate additional isolation valve, which in combinationwith the requirement of the pulse width modulated compressor, increasesthe overall cost of the refrigerant system.

SUMMARY OF THE INVENTION

In disclosed embodiments of this invention, a compressor is providedwith a pulse width modulation control. In one embodiment, a suctionmodulation valve is controlled in pulse width modulation manner tocontrol the flow of refrigerant to the compressor. In a secondembodiment, the pressure to a back pressure chamber of a scrollcompressor is changed in a pulse width modulation manner to engage anddisengage the scroll elements. With both embodiments, the expansiondevice positioned between the condenser and the evaporator is preferablyan electronic expansion device, which can be rapidly cycled from an openposition to a closed position. When the compressor is in an “off”position due to the pulse width modulation control, the expansion deviceis also predominantly closed. When the compressor is in an “on” positiondue to the pulse width modulation control, the expansion device ispredominantly open. In this manner, refrigerant flow between thecondenser and the evaporator is instantly interrupted. Therefore, thepressure fluctuation problem mentioned above is addressed without therequirement of having an isolation valve. Please note that, in thecontext of this invention, the compressor “off” position refers to asituation when the scroll elements are disengaged from each other andlittle or no compressor is taken place. Similarly, the “on” positionrefers to a situation where the compressor elements are engaged and thescroll compressor is compressing the refrigerant moving it fromevaporator to condenser.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic refrigerant system incorporating the firstembodiment of the present invention.

FIG. 2 shows a compressor, as utilized in a second embodiment of thepresent invention.

FIG. 2A shows a refrigerant system with the FIG. 2 compressor.

FIG. 3 is a graph showing pressure fluctuations for the prior art andthe present invention system and control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A refrigerant system 20 is illustrated in FIG. 1 and includes acompressor 22 compressing a refrigerant and delivering it to adownstream heat exchanger 24. Heat exchanger 24 would act as a condenserin a cooling air conditioning mode of operation, and is an outdoor heatexchanger. While the present invention is illustrated as an airconditioning system, it should be understood that the invention wouldalso extend to heat pumps, and other applications (e.g., refrigerationapplications). Also, it has to be understood that a basic refrigerantsystem shown in FIG. 1 (and FIG. 2A) may have various options andfeatures to enhance its operation and control (including vaporinjection, bypass unloading, various dehumidification schemes, tandemcompressors, multi-circuit arrangements, variable speed components,etc.). All these system design variations are within the scope and canequally benefit from the present invention.

An expansion device 26 is positioned downstream of the heat exchanger24. The expansion device 26 may be an electronic expansion valve, whichcan be rapidly cycled between an open and closed position to control theamount of refrigerant flowing through the expansion device 26. A heatexchanger 28 is positioned downstream of the expansion device 26. Theheat exchanger 28 is an indoor heat exchanger, and provides the functionof an evaporator in a cooling air conditioning mode of operation.Refrigerant flowing from the heat exchanger 28 passes through a suctionmodulation valve 30, and back to the compressor 22. A control 32provides a pulse width modulation control to both suction modulationvalve 30 and electronic expansion valve 26. The suction modulation valve30 is rapidly cycled between opened and closed positions to control theamount of refrigerant flowing to the compressor, when the control 32determines that the refrigerant system 20 should operate in a reduced(part-load) capacity mode. The control logic and timing when suchcontrol would be actuated, and the detail of the control and design ofthe valve 30 are known in the art. What is inventive here is that thecontrol 32 simultaneously controls the expansion valve 26 such that itis predominantly biased toward the closed position when the valve 30 isbiased toward closed position. In this manner, the heat exchangers 24and 28 may essentially have no flow communication when the mass flow ofrefrigerant reaching the compressor is reduced.

FIG. 2 shows another embodiment 301 wherein the compressor is a scrollcompressor having a non-orbiting scroll member 304 and an orbitingscroll member 302. As known, a back pressure chamber 306 may receive apressurized fluid from a source 308 and through a flow (e.g., solenoid)valve 310. The control 312 controls the opening and closing of the valve310 using the pulse width modulation method. By rapidly opening andclosing the valve 310 the pressure in the back pressure chamber 306 iscycled between high and low values. When the back pressure chamber issubjected to a high pressure, this pressure forces the non-orbitingscroll 304 against the orbiting scroll 302, essentially eliminating anyleak bypass of compressed refrigerant through the compression elements.Thus, refrigerant is compressed in the compressor and deliveredthroughout the system. When the valve 310 blocks flow of high pressurerefrigerant to the back pressure chamber 306, the lower force in theback pressure chamber 306 allows the scroll elements 304 and 302 to moveaway from each other, creating a significant gap between the orbitingscroll 302 and non-orbiting scroll 304, resulting in minimal or norefrigerant compression in the compressor 301. This structure is shownschematically, and is generally known in the art. Many of the variationsof this concept (including a pulse width modulation technique applied todifferent compressor types) are known in the art and are within thescope of the present invention. The control 312 also communicates withthe expansion device 26 in this embodiment in a manner similar to theFIG. 1 embodiment, and as shown in the circuit 120 in FIG. 2A.

By controlling the expansion device 26, in conjunction with the suctionmodulation valve 30 of the FIG. 1 embodiment or with the valve 310 ofthe FIG. 2 embodiment, the potential excessive pressure fluctuationproblem, present in the prior art can be controlled and eliminated. FIG.3 shows P_(cond) and P_(evap), as the fluctuating pressures in thecondenser and evaporator accordingly without the pulse width modulationcontrol of the expansion device 26. Further, the P′_(cond) and P′_(evap)are the pressures in the condenser and evaporator accordingly, showingsignificant reduction in magnitude of pulsations, with the pulse widthmodulation control of the expansion device 26 provided by the presentinvention.

As stated above, the electronic expansion device 26 is cycled in a pulsewidth modulation manner between essentially open and closed positions,in synchronized relation with the opening and closing of the suctionmodulation valve 30 or valve 310, to reduce pressure fluctuationsthroughout the system and consequently improve operational efficiencyand an occupant's comfort in the conditioned space. It should be notedthat the open and closed positions for the expansion device 26 are notnecessarily correspond to fully open and fully closed positions. Forinstance, a partially closed position for the electronic expansiondevice 26 may serve the purpose of reducing pressure fluctuations to anacceptable level. Furthermore, synchronization of the operation for theflow control devices 26 and 30 (or 310) is valuable, although it may bebeneficial to slightly delay closing of the electronic expansion device26 to allow some refrigerant flow generated by flow inertia to pass to alow pressure side of the refrigerant system. For the same reason, thecycle time interval for the expansion device 26 may be slightlydifferent than for the flow control devices 30 or 310. In general, atypical cycle time for the flow control devices 26 and 30 (or 310) mayrange from 5 seconds to 30 seconds. A typical delay time may be on theorder of 2-3 seconds and would largely depend on a refrigerant systemsize (or internal volume).

It should also be noted that the open and closed position of the suctionmodulation valve 30 (or the valve 310) may not necessarily correspond tothe maximum possible opening or the minimum possible closure of thisvalve. The pressure fluctuations can be especially important on the highside of the refrigerant system (a condenser portion of the refrigerantsystem), where the refrigerant is at a higher pressure, than on thelower side, and thus the magnitude of the pressure fluctuations on thehigh side is normally higher then the magnitude of the pressurefluctuations on the low side (an evaporator portion of the refrigerantsystem). As known, pressure fluctuations can be detrimental in obtainingdesired temperature and/or humidity control within the conditionedenvironment and need to be reduced to the acceptable level. The desiredtemperature and/or humidity control within the conditioned environmentis achieved by reducing the pressure fluctuations as described above.Another potential problem associated with the pressure fluctuations inthe refrigerant system is that these pressure fluctuations introduceunwanted, and sometimes excessive, vibrations of various systemcomponents, often leading to the failure of these components. A highvibration level can also generate undesirable noise. In this case, areduction in the vibration level can be achieved by coupling feedbackobtained from the operation of the valve 30 (or 310) and the electronicexpansion valve 26. The feedback control can establish the mostappropriate operation of these components relying on the input from avibration sensor 44. This vibration sensor 44 can be installed atcertain specific locations in the refrigerant system. As an example, thesensor 44 can be installed on the discharge line 42, and the electricsignal of this sensor corresponding to the vibration level can becommunicated to the control 32 (or 312).

Thus, the present invention without the requirement of any additionalflow control devices, or other extra hardware, addresses theabovementioned problem of excessive pressure fluctuations on the highand low pressure sides of the refrigerant system.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill would recognize that certain modificationswould come within the scope of this invention. For that reason thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A refrigerant system comprising: a compressor for compressing arefrigerant and delivering the refrigerant to a first heat exchanger,refrigerant passing from said first heat exchanger through an expansiondevice, into a second heat exchanger, refrigerant passing from saidsecond heat exchanger back to said compressor; and a pulse widthmodulation control for rapidly modulating the flow of refrigerant fromthe compressor between high and low flow positions, said control alsousing pulse width modulation for moving said expansion devicepredominantly toward a closed position when the compressor is in saidlow flow position and moving said expansion device predominantly towardan open position when the compressor is in said high flow position. 2.The refrigerant system as set forth in claim 1, wherein said expansiondevice is an electronically controlled expansion device.
 3. Therefrigerant system as set forth in claim 1, wherein a suction modulationvalve is positioned between said second heat exchanger and saidcompressor, and said suction modulation valve being controlled torapidly open and close to adjust the flow of refrigerant to saidcompressor between the high and low flow positions.
 4. The refrigerantsystem as set forth in claim 1, wherein said compressor being a scrollcompressor, and having a back pressure chamber, which is rapidly cycledbetween high and low pressure conditions to move said compressor betweenthe high and low flow positions.
 5. The refrigerant system as set forthin claim 1, wherein said expansion device is moved to a fully closedposition when the compressor is in said low flow position.
 6. Therefrigerant system as set forth in claim 1, wherein a pulse widthmodulation cycle time is between 2 and 30 seconds.
 7. The refrigerantsystem as set forth in claim 1, wherein an expansion device time in saidclosed position is different from a compressor time in said low flowposition.
 8. The refrigerant system as set forth in claim 7, whereinsaid time difference is between 1 and 3 seconds.
 9. The refrigerantsystem as set forth in claim 1, wherein the expansion device cycle isdelayed with respect to the compressor cycle.
 10. The refrigerant systemas set forth in claim 9, wherein said delay is between 1 and 3 seconds.11. The refrigerant system as set forth in claim 1, wherein vibration onat least one component in the refrigerant system is monitored, and themonitored vibration being utilized to adjust at least one operationalparameter of at least one of the pulse width modulated expansion deviceand the pulse width modulated refrigerant flow from the compressor. 12.The refrigerant system as set forth in claim 1, wherein pressurefluctuation control is provided to tightly maintain at least one oftemperature and humidity in an environment to be conditioned.
 13. Therefrigerant system as set forth in claim 1, wherein the pulse widthmodulation of the expansion device and the pulse width modulation of therefrigerant flow from the compressor are provided to control and limitpressure fluctuations within said first heat exchanger, within saidsecond heat exchanger or within both said first and said second heatexchangers. 14.-25. (canceled)
 26. A refrigerant system comprising: acompressor for compressing a refrigerant and delivering the refrigerantto a first heat exchanger, refrigerant passing from said first heatexchanger through an expansion device, into a second heat exchanger,refrigerant passing from said second heat exchanger back to saidcompressor; and a pulse width modulation control for a suctionmodulation valve positioned between said second heat exchanger and saidcompressor, and said suction modulation valve being rapidly modulatedbetween open and close positions to adjust the flow of refrigerant tothe compressor and said control also using pulse width modulation tomove said expansion device predominantly toward a closed position whenthe suction modulation valve is moved toward a closed position and tomove said expansion device predominantly toward an open position whenthe suction modulation valve is moved toward an open position.
 27. Arefrigerant system comprising: a compressor for compressing arefrigerant and delivering the refrigerant to a first heat exchanger,refrigerant passing from said first heat exchanger through an expansiondevice, into a second heat exchanger, refrigerant passing from saidsecond heat exchanger back to said compressor, and said compressor beinga scroll compressor, and having a back pressure chamber, which israpidly cycled by a control using pulse width modulation, to movebetween high and low pressure conditions to move said compressor betweenhigh and low flow positions and said expansion device also beingcontrolled by pulse width modulation and being moved predominantlytoward a closed position when said compressor is in said low flowposition and being moved predominantly toward an open position when saidcompressor is in said high flow position.